1. Field of the Invention
The present invention relates to an image readout apparatus such as facsimile machine, image scanner, or the like; and an imaging lens for image readout employed in an optical system thereof. In particular, the present invention relates to a four-group, six-element imaging lens in which first and second lenses are cemented to each other, and fifth and sixth lenses are cemented to each other.
2. Description of the Prior Art
Conventionally, a solid-state image sensor made of CCD has been used in general as a photosensitive member disposed in an imaging section of an image readout apparatus such as facsimile machine, scanner, or the like. Recently, as the pixel density in CCD has rapidly been increasing, imaging lenses with a higher resolution have been demanded as those employed in the image readout apparatus.
As an imaging lens which can respond to such a demand, a six-element image readout apparatus disclosed in Japanese Unexamined Patent Publication No. 10-253881 has been known.
In the prior art disclosed in the above-mentioned publication, however, a greater depth is hard to obtain as the resolution of the imaging lens becomes higher, whereby a higher degree of focus adjustment is required in the image readout apparatus.
Also, there has been a fear of the resolution deteriorating due to fluctuations in flatness of an original or due to the flotation thereof.